Improved safety for integrated granulation and drying suites
Extensive safety testing confirms pressure enhancement effects and
identifies safe design limits for integrated granulation and drying systems.
GEA Pharma Systems in conjunction with the FSA, the safety specialist
centre in Germany, have carried out an extensive test programme involving over
100 test explosions. This research has shown conclusively that should an
explosion occur during the transfer operation in an integrated system where a
granulator is connected directly to a fluid bed dryer without an explosion
isolation valve, the secondary explosion pressures in the granulator can be
significantly higher than in the fluid bed. These tests have enabled Niro
Pharma Systems to gain full EC type approval for a range of pressure shock
resistant integrated systems and 16-bar pressure shock resistant high shear
granulators.
Safety when using organic solvents
The tests were
carried out with hybrid mixtures that behave in the same way as pharmaceutical
products containing organic solvents and showed that the final explosion
pressure in the granulator is dependent on the volumes of the two vessels and
that the length and diameter of the interconnecting duct is critical in
ensuring that the pressure remains within safe limits.
The tests showed that where the fluid bed is designed in accordance with VDI
2263 part 5 (i.e.: for a 10-bar explosion pressure, which the standard
considers to be adequate for all pharmaceutical powders and organic solvent
combinations), then the granulator must be able to withstand an over pressure
of at least 16 bar to provide a range of transfer duct configurations which are
both practical and safe.
Where the fluid bed is required to handle materials with explosion pressures
greater than 10 bar (e.g.: metal powders) - and hence is designed outside of
the VDI standard - or where the configuration of the interconnecting duct is
outside the safe design parameters, then either the granulator must be designed
to a higher pressure shock resistance or a hygienic fast acting valve, or some
other form of protection, is essential.
The test program showed
that the pressure enhancement effects are caused by the difference in the
propagation speed between the pressure wave and the flame front. The worst
cases are when the pressure in the granulator is able to rise significantly
before the flame can reach it and ignite the pre-compressed material. For the
range of transfer duct configurations to be used with the 16-bar granulator
design, the presence of bends and obstructions such as mills was not seen to
affect the increase in pressure. For plant processing powders, or mixtures that
are not flammable at the time of transfer between the granulator and the fluid
bed, then the risk of explosion is eliminated and hence a wider range of
transfer duct designs can be used safely.
This extensive research program has significantly advanced the state of the
art in safety technology for pharmaceutical plants and confirms GEA Pharma Systems
Systems’ commitment to introducing new products which are based on sound
research and development using solid process know how and understanding.